(a) Field of the Invention
The present invention relates to a wireless LAN (Local Area Network) distribution system and an embodiment method thereof. More specifically, the present invention relates to a location management server, an Ethernet-based LAN distribution system comprising the local management server, and an embodiment method thereof.
(b) Description of the Related Art
Wireless LAN, initially developed just as an alternative to a wire LAN, is now being taken into consideration as an important wireless Internet access means, with the advent of the IEEE 802.11b standard that supports a data transmission rate of up to 11 Mbps at 2.4 GHz.
In addition, development has occurred for the conventional wireless Internet for mobile communication networks, but difficulties exist in extending services due to its low data transmission rate and high price for use. Contrarily, wireless LAN using an unlicensed band, ISM (Industrial Scientific and Medical), and relatively inexpensive equipment supports a high data transmission rate with a low price for use. Hence, the wireless LAN has recently become an important means for wireless Internet centering around a hot spot area due to those strong points.
In the wireless LAN, a station (hereinafter referred to as “STA”) having a wireless interface is connected to a wire network through an access point (hereinafter referred to as “AP”) having the same wireless interface as a second STA.
For multiple APs present in one sub-net, they are connected through a wireless LAN distribution system (hereinafter referred to as “DS”). Namely, connections between APs and between an AP and other networks are through the DS.
In the IEEE 802.11 standard, which has been widely used in recent years, however, the DS is defined but the details of its embodiment are not prescribed. In actuality, the embodiment of the DS relies on the individual manufacturers' standards.
Although they differ depending on the capability of the APs, the currently used methods are a method in which all the APs on the DS perform an address resolution protocol (hereinafter referred to as “ARP”) function, and a method in which an edge router performs an ARP and each AP performs a proxy ARP on behalf of STAs, or each STA directly sends an ARP response.
FIG. 1 illustrates an example of a representative Ethernet-based wireless LAN distribution system comprised of four APs.
The DS includes, as shown in FIG. 1, a plurality of APs 105-1 to 105-m connected to an IEEE 802.3 Ethernet 104, as is now most widely used.
More specifically, the DS comprises a correspondent node (hereinafter referred to as “CN”) 101 connected to an Internet network 102 for sending data to an STA 106, a public or private Internet network 102, an edge router 103 responsible for a subnet comprised of APs 105-1 to 105-m, a wireless LAN distribution system 104 operated according to the IEEE 802.3 standard, m APs 105-1 to 105-m each connected to the same wireless LAN distribution system 104, and an STA 106 receiving the data in the end.
The data-forwarding process of the above construction will now be described. The data sent from the CN 101 to the destination STA 106 are first forwarded to the edge router 103, to which the destination STA 106 belongs, via the Internet network 102 using Internet protocol (hereinafter referred to as “IP”) routing. The edge router 103 simply broadcasts the received data to the wireless LAN distribution system 104. Then the individual APs check a destination IP address for the broadcast data, perform an ARP to search for a destination media access control (hereinafter referred to as “MAC”), and finally send the data to the STA 106.
FIG. 2 is a timing diagram of the conventional Ethernet-based wireless LAN distribution system for association and data reception, in which the steps S201 and S202 involve association, and the steps S203 to S206 involve data reception.
In the association procedures, the STA 106 entering the area of a specific AP sends an association request message when it is in a power-up state; a reassociation request message when it is moved from another AP; or a disassociation request message when it disconnects the existing connection, in step S201. These request messages include the MAC address of the STA.
Upon receiving the (re)association or disassociation request message from the STA, the AP generates, maintains, or deletes a list of STAs in its area, in step S202.
In the data reception procedures, the CN 101 sends data to a specific STA as a destination, and the transferred data are first forwarded to the edge router 103 via the Internet network 102, in step S203. The IP address of the destination STA is known but the MAC address for final forwarding is unknown to the edge router 103. So, the edge router 103 broadcasts the data to the wireless LAN distribution system 104 so that the wireless LAN distribution system 104 forwards the data to all the APs 105-1 to 105-m, in step S204.
Upon receiving the data from the edge router 103, each AP performs a check for the IP address of the received frame and then an ARP to determine the destination MAC address, in step S205. Subsequently, the APs forward the data to the AP with the finally mapped MAC address as the destination, in step S206.
In this way, in the conventional wireless LAN distribution system, all the APs must perform an IP address check and an ARP for the packet sent to an STA not present in their area, because there is no location management for the STA in the distribution system. This problem may be solved in a network comprised of a small number of APs, but it causes unnecessary processing for each AP in a network with a substantial number of APs to thereby increase the processing load of the whole network, and consumes a relatively high processing power for the APs which raises the price of the APs.
Additional methods include one in which each AP in the wireless LAN distribution system may perform a proxy ARP in place of the STA belonging to its area, or a method in which the STA directly sends an ARP response to the ARP request of the edge router. In those cases, the ARP cache managed by the edge router becomes excessively large, and the traffic load of the whole network may explode because all the APs in the wireless LAN distribution system have to periodically perform an ARP or all the STAs in the wireless LAN distribution system have to make an ARP response.
Particularly, in an environment in which the STA is mobile, the mapping table at the edge router updated by a periodic ARP is possibly unmatched to the actual location of the STA, thus disabling the data-forwarding.
A related approach is Application No. 5768531 under with the title “Apparatus and methods for using multiple communication path in a wireless LAN” by Isabel Y. Lin, in which a specific STA is enabled to forward data directly to a destination STA belonging to the same AP, thereby reducing the traffic load of the wireless LAN distribution system. But this method also has a problem in that data forwarding is disabled in an environment in which the STA is mobile.